Photo-controlled permeation of spiropyran modified gramicidin A ion channel

Abstract

Biomimetic devices show great potential as being molecular sensors of biological species. Gramicidin A (gA) is a well studied ionophore that can be easily modified at the C-terminus to be incorporated into phosphotidylcholine bilayer membrane systems. Potassium permeation of modified gA attached to spiropyran can be controlled with light. Upon ultra-violet irradiation spiropyran transforms to the more polar form merocyanine. The process back to spiropyran is completely reversible upon irradiation with 550 nm light or thermally. Free bilayer membrane vesicles are employed to describe the characteristics of modified ion channels. Characteristics of gA modified with spiropyran are described herein. A device has been created and characterized using electrochemical impedance spectroscopy to analyze potassium permeation through a tethered bilayer membrane system (tBMS) on a sheet of gold utilizing sulfur anchors. The device consists of a tethered phase and a mobile upper phase. The mobile lipid layer incorporates gA modified with spiropyran. The modification allows for control of potassium permeation across the tBMS. Impedance analysis shows good agreement with the ability to control potassium permeation to that of the free vesicle.